As a method for forming a high-quality semiconductor film, there is an epitaxial growth technique which grows a single-crystal film on a substrate, such as a wafer, using vapor phase growth. In a vapor phase growth apparatus using the epitaxial growth technique, a wafer is placed on a support portion in a reaction chamber which is maintained at atmospheric pressure or reduced pressure. Then, a process gas, such as a source gas which will be a raw material for forming a film, is supplied from, for example, a shower plate that is provided at an upper part of the reaction chamber to the surface of the wafer while the wafer is being heated. The thermal reaction of the source gas occurs in the surface of the wafer and an epitaxial single-crystal film is formed on the surface of the wafer.
In recent years, a gallium nitride (GaN)-based semiconductor device has drawn attention as a material of a light emitting device or a power device. There is a metal organic chemical vapor deposition method (MOCVD method) as an epitaxial growth technique for forming a GaN-based semiconductor film. In the metal organic chemical vapor deposition method, organic metal, such as trimethylgallium (TMG) trimethylindium (TMI), or trimethylaluminum (TMA), or ammonia (NH3) is used as the source gas.
The MOCVD method bubbles or sublimates liquid or solid organic metal stored in a storage tank with gas such as hydrogen, to generate a source gas including organic metal and supplies the source gas to a reaction chamber. However, since the saturated vapor pressure of organic metal is relatively low, it is difficult to stably supply an organic-metal-containing gas. JP H4-114728 discloses a technique which prevents the condensation of a source gas in a pipe.